SpringA powerful free cross-platform RTS game engine. - Report issues at https://springrts.com/mantis/
Warzone2100Command the forces of The Project in a battle to rebuild the world after mankind has been nearly destroyed by nuclear missiles. A 100% free and open source real-time strategy game for Windows, macOS, Linux, BSD+
OpenraOpen Source real-time strategy game engine for early Westwood games such as Command & Conquer: Red Alert written in C# using SDL and OpenGL. Runs on Windows, Linux, *BSD and Mac OS X.
MyRTSMultiplayer RTS game prototype written in Java using LibGDX
realtimechessIn Real-time Chess (or Kung-Fu Chess, Ninja Chess), all pieces can be moved simultaneously!
auroraA small entity-component-system game engine for real-time-strategy games.